Apple's press event invitations are works of art. On the surface they're clear, but they usually have a deeper meaning that is intended to make sense only after the big reveal. It's a way that Apple generates even more interest about its announcements. When people are clamoring for any clue they can, they get a single image or phrase from Apple, an official but obfuscated message from on high, which inspires another fresh round of speculation about what surprises will be revealed at the event.
This year's iPhone event invitation is clever and simple, but with a single data point which has caused a lot of discussion:

The date, time, and place icons are all straightforward. The phone icon with a '1' badge has got analysts and pundits alike wondering if we're getting a single phone this season, and the camps are split on whether it's the 4s or the 5.
I think we're missing the point.
When Apple puts a clue into an invitation, it's a clue about a feature or other positive. Hinting about a single phone amidst widespread speculation about two phones is lowering expectations, and this is not in keeping with Apple's track record on how they use invitations. If one wanted to be so literal, they might also note that the '1' badge would only appear on an iPhone if someone missed a call, or if there was a voicemail waiting, but of course those don't make sense in this scenario, so we're left to guess, and I think most folks are guessing wrong.
So what does the '1' mean? Yes, it means one phone. But not '4s or 5'. It means GSM+CDMA.
One phone for the world. One phone for all 288+ carriers.
One phone for the user. One phone for a person regardless of whether they decide to switch carriers after a year or two.
As for the 4s vs. 5 debate, I'm still firmly in the 'both' camp but, as I've said before, the 5 will be the star of our show. The 4s will be mentioned as a welcome revision to an old model, making it an excellent low cost option.
Which is more likely, that Apple would put a '1' where we're expecting and hoping for '2' (models) or that they'd use a '1' where '1' is better than the current '2' (GSM and CDMA)? I guess we'll see.
Happy Christmas Eve!
PS: For those coming here for the first time, here are my predictions for what Apple will be announcing and a short follow-up.